Cooling water treatment and compositions useful therein



United States The present application is a continuation-in-part ofapplication Ser. No. 266,193 which was filed on Mar. 19, 1963, nowabandoned.

The invention is directed to a process for the treatment of coolingwater to make the water less corrosive and to minimize the fouling ofmetal heat exchange surfaces caused by the deposition of alumina flocand other materials carried in suspension in the water. Moreparticularly,

the subject invention relates to cooling water compositions whichcontain both phosphates and modified tannins.

River water is usually relatively low in hardness and high in turbidity.This turbidity may consist of suspended clay and other forms ofsuspended silt, microbiological growths, iron and other suspendedsolids. Turbid water, whether it be river water or water from some othersource, usually is clarified with alum and/or sodium aluminate before itis used as the recirculating cooling liquid in cooling systems. Thecommonly used clarification plant settling beds are somewhat ineflicientand the settled solids, which include alumina floc, are easily disturbedby current and thermal gradients. Some of the precipitated alumina flocand other solids often are carried over into the makeup water forrecirculating cooling systems. The total concentration of alumina flocand solids and this water may be only a few parts per million but,circulating in the system, they tend to agglomerate into largerparticles and stick on surfaces of the cooling system, such as coolingtower decks, and especially on heat transfer surfaces. Also, theparticles of alumina fioc include and absorb other suspended matter,such as microbiological growths, corrosion products, silt, and the like.Over a period of time these suspended solids in the recirculatingcooling water build up a voluminous, fiocculent deposit which canseverely reduce heat transfer coeflicients and impede water flow throughheat exchangers. Although the deposit is very light in density, itadheres tightly to hot metal surfaces and is not readily removed bysimply increasing the water velocity through heat exchanger tubes duringnormal operations. It is accordingly a need in the field of watertreatment to provide a combination of compatible chemicals in thecooling water which will keep suspended alumina floc in the coolingwater and simultaneously minimize corrosion of the metal heat transfersurfaces and other component metal parts of the cooling system.

In general, it has been found that the corrosion and fouling of metalheat transfer surfaces coming in contact with cooling water can becontrolled through the use of a composition containing both phosphatesand modified tannins. The phosphates and modified tannins can be addedto a cooling water separately, or they may be combined into a singleproduct in either granular or powdered form or in the form of a shapedarticle of manufacture, e.g., a water treating ball. One of theadvantages of the subject compositions is that they can be formedreadily into compact balls which can be added conveniently to thecooling water.

The phosphates which can be used in the water treating compositions ofthe subject invention include the following: orthophosphates,pyrophosphates such as tetratripolyphosphate, any of the water-solublepolyphosphate atent O sodium pyrophosphate, tripolyphosphates such assodium ice any of the alkali metals, alkaline earth metals, zinc, orcadmium including those known as hexametaphosphates and glassyseptaphosphates. The use of phosphates in cooling water systems isdescribed in a patent to Pink et al., U.S. 2,358,222.

The modified tannins can be produced from all types of natural tannins.Mixtures of tannins may also be used in preparing the subjectcompositions. The color reactions of tannins are used in theiridentification and classification. The tannins have been divided intotwo principal groupsthe catechol tannins and the pyrogallol tannins.After dry distillation the catechol tannins yield catechol as aprincipal product of decomposition, and the pyrogallol tannins after drydistillation yield pyrogallol. Solutions containing catechol give agreenish-black precipitate with ferric salts, whereas solutionscontaining pyrogallol tannins give a bluish-black precipitate withferric salts. In general, only pyrocatechol derivatives are found incatechol tannins, whereas gallic acid is always present in pyrogalloltannins. The preferred tannins for use in the subject process are thecatechol tannins although pyrogallol tannins can also be used in theprocess.

Natural tannins can be obtained from a number of materials. One of theprincipal sources in the quebracho trees, the wood of which containsabout 20 to 23% of easily extractable tannin of the catechol type. Othersources include chestnut wood, divi-divi pods, mangrove bark cutch (oneof the preferred sources along with quebracho trees), wattle bark,gallnuts, hemlock bark, sumac, and oak bark.

A discussion of tannins and tannin chemistry is set forth in theEncyclopedia of Chemical Technology, vol. 13, pages 578 to 599, whicharticle is included as part of the subject disclosure.

In the modification step the tannins are reacted with an aqueoussolution of a salt of sulfurous acid of the group consisting of thesalts of ammonium, potassium and sodium sulfite and bisulfite, or aremodified by reaction with sodium or ammonium cyanides, with sodiumchloroacetate, with sulfuric acid (either sulfonation or oxidation),with nitric acid (which would involve either oxidation or nitration),etc., to product functional group changes in the natural tannin wherebyits performance is markedly improved as an aid to the phosphatetreatment.

A preferred group of modified tannins which can be used in the subjectinvention is described in U.S. Patent 2,831,022. In the processdisclosed in this patent Western hemlock bark or barks of like chemicalcharacteristics are digested at elevated temperatures in the presence ofsuitable amounts of aqueous ammonium, sodium, or potassium sulfite orbisulfite or mixtures of these silutions until compositions composed ofextracts and derivatives are formed from the naturally occurring tanninscontained in the bark. Pieces of bark are desirably reduce-d in size topass screens of about 4 to 20 meshes to the inch prior to the digestionstep. The digestion temperature can range from about 50 C. to about 200C. Digestions which are both rapid and relatively efiicient are obtainedat temperatures of from about C. to about C. According to .Patent No.2,831,022 digestion periods of about 0.5 hour to about 4.0 hours can beused, but in all cases digestions are stopped while there still remainssome content of sulfurous acid salt in the charge. It is also pointedout in the patent that a smaller proportion of the alkali sulfurous acidsalt than that equivalent to about 0.01 part of sulfur dioxide per partof oven dry bark is insufficient, while more salt than that equivalentto about 0.30 part sulfur dioxide per part of oven dry bark is in excessof that needed to carry out the reaction satisfactorily. It is likewisepointed out, however, that an excess of the latter proportion can beused provided inorganic salts resulting from such excessive amounts arenot deleterious in the solutions of watersoluble products derived fromthe process. The disclosure of US. Patent 2,831,022 is included in thesubject specification by reference. In the instant process tannins fromsources other than hemlock bark which are modified as described in US.Patent 2,831,022 also can be used with great success.

The ratio of phosphates to modified tannins should be in the range offrom about 1:4 to 4:1 in the final composition. The compositionpreferably is applied to water in sufiicient quantities to give aphosphate concentration of from 1 to 100 p.p.m. express as P Thepreferred pH range of application is 6.5105, although a pH of frclim 5.5to 7.5 may still be used with satisfactory resu.ts.

Other materials may be added to a phosphate-modified tannin in order toincrease the performance of the composition under special circumstances.Where copper or nickel alloys come in contact with the cooling water,for example, Z-mercaptobenzothiazole may be added .to improve theperformance. The use of these additional materials, however, is notconsidered a part of the subject inventiomVarious anionic inhibitorssuch as the well known chromates can also be added to the composition.

The exact nature of the activity of the combined modified tannins andphosphates on mild steel and Admiralty test specimens in a variety ofwaters is not fully known. It is known, however, that hardness in waterplays an important part in the corrosion protection of mild steel withphosphate-based treatments. It is believed that precisely the rightamount if calcium is needed to transport the condensed phosphate ionsthrough the diffuse double layer to sites whereat dissolution of iron istaking place. The escaping iron at relatively high concentration at thesurface catalyzes the hydrolysis of the condensed phosphate exposingreactive orthophosphate groups in close proximity to the metal surface.The freshly formed orthophosphate is chemisorbed onto the developingcubic oxides, controlling oxide form and rate of growth. The resultingprotective film, which is largely iron oxides, has small amounts of bothcalcium and orthophosphate trapped in a thin outer layer. This outerlayer is believed by some to be a calcium iron phisphate compound.

If the ratio of calcium ions to potential orthophosphate ions insolution or in double layer is too high then the condensed phosphatepolyion may become blocked by' counterions to the extent that thephosphate is no longer able to function in the above manner. This may bedue to retarded hydrolysis rates at the metal surface or reducedactivity of the released orthophosphate in the presence of the increasedcalcium concentration. Reaction rates here apparently are extremelyimportant. It has been found that the proper balance can be restored incases of high calcium content through the use of the modified tanninswhich are described above. These materials act as organic dispersingagents which, because they are anionic polyelectrolytes of the propermolecular weight and configuration, are capable of competing forcounterions as well as adsorbing on nuclei and colloidal particles,particularly hydroxides, which might otherwise inactivate the phosphate.The phosphate must be able' to make a close approach to the metalsurface in an, active form.

Almost all natural tannins react with iron andbecome inactive. Themodified tannins used in the subject process, however, have a much lowersusceptibility to iron-inactivation. 7

Phosphates also react with iron. Hydroxides such as composition seems toplay a part in the degree of corrosion protection obtained.Orthophosphate is believed to be the active form, but if added as suchit is quickly inactivated before it can reach the surface in sufiicientquantity to be truly efiective. Pyrophosphate, the dimer oforthophosphate, is a very effective inhibitor when combined with themodified tannins. Its higher degree of effectiveness stems from thefact-that one mol on hydrolysis immediately gives two mols oforthophosphate. Further, its comparatively small size, even with anyundissociated counterions, allows fairly rapid transport. The morehighly condensed phosphates do not have as high mobility as the tpyroform, nor do they revert to orthophosphate as rapidly at the surfacewhere needed. The more highly condensed phosphates have a greatertendency to complex iron in solution any may actually increase thecorrosion rates observed.

In very hard water, a combination of phosphates may be best. In eachcase, however, it is helpful to have pyrophospha-te in the blend. Thepyrophosphate would provide the fast reactivity and mobility required,while the higher phosphate would provide the holding power. Thefollowing examples will serve to illustrate the subject invention.

Example I This example shows one method which can be used to modifytannins. Inthe method, grams of mangrove tannin was dissolved in ml. ofdistilled water. A second solution was formed by dissolving 16.6 gramsof Example II This example illustrates a second method which can be usedto produce the modified tannins of the subject in vention. In thismethod, 50 grams of chestnut tannin was mixed with 0.1 gram of V 0 0.5ml. of ethyl silicate 40, and 1- ml. of distilled water. Thechestnuttannin had previously passed through an ion exchange resin to removecations. Twenty-five (25) ml. of concentrated sulfuric acid was added tothe above mixture and the mixture was allowed to react in its own heatfor 20 minutes. After 20 minutes, 275 ml. of distilled water wasintroduced into the reaction mixture. Initially a thick paste was formedwhich thinned as more water was added.

Twenty-five (25) ml. of .isopro'panol wasadded to precipitate thereaction product. The precipitate on filtration gave a black-brown cake.The cake was solubilized in water by raising its pH to above 11 withcaustic. The solution was diluted to 500 ml. with distilled water andthis product was used in conjunction with phosphates in the treatment ofcooling waters. i

The tannins can be reacted with nitric acid in a manner similar tosulfuric acid. In both cases the reaction is a nitration or sul'fonationand/or oxidation reaction. Likewise, the modification can be carried outthrough the use of sodium, potassium or ammonium syanide or sodium,pota'ssium or ammonium thiocyanate in which case the modificationprocedure would be carried out in a maniron or aluminum hydroxide absorbphosphate ions from solution increasing sludging, scaling and fouling.The

modified tannins absorb on the colloidal hydrous oxides and prevent thedepletion of the phosphates.

The type of phosphate used in the modified tannin ner similar to thatshownabove in connection with sodium chloroacetate. As a substitute forsodium chloroacetate one can use any sodium or potassium haloacetate,halopropionate orhalobuty rate. The preferred halogens are chlorine,bromine and iodine. As has been indicated previously, the tannins canalso be modified by the method shown in US Patent 2,831,022. Thesul'fite or bisulfite modification shown in the patent constitutes thepreferred modification process in the subject invention. In thebisulfite treatment, the reaction is carried out initially at a moderatepH (5-7) whereby the bisulfite addition takes place with the oxy ringstructure being split to form additional -OH groups. The solubilizing ofthe product With caustic preferably is then carried out undersutficiently mild condition (pH of 89) so as not to cause the prodnot tohydrolyze or to revert to its original condition. Potassium or ammoniumsulfite or bisulfite can be substituted for sodium sulfite or bisulfitein the process. As was indicated above, any natural tannin may besubstituted for the hemlock tannin of US. Patent 2,831,- 022. Thepreferred tannins, however, are the mangrove and/ or quebracho tannins.

Example III Example 1 of US. Patent 2,831,022 is reproduced here asshowing a preferred method of producing modified tannin.

A batch of 14.1 lb. ground western hemlock (Tsuga heterophylia) bark(all of which passed a wire screen having openings inch by 1 inch,equivalent to 6.0 lb. oven-dry bark) was mixed with 45.6 lb. water and145.8 gm. sodium metabisulfite (Na S O The latter (which contained 5.7%moisture) is equivalent to 150.2 gm. sodium bisulfite (NaHSO which isjust as suitable as, and can be used instead of, the metabisulfite inthis example. The mixture was heated to 85 C. and digested at thattemperature for 2 hours. A considerable amount of the sodium sulfiteremained. The mixture resulting from this digestion was drained and thesolids were washed by showering hot water on the solids retained on afilter screen. The drainings and washings were filtered. The filteredsolution of reaction product was concentrated to 40% solids at anabsolute pressure of 5 lbs. per sq. in. and subsequently spray dried,leaving a watersoluble solid which when ground to a powder was darkreddish brown. Analysis of the filtered solution showed a gross yield ofsolids of 14.4% of the weight of the ovendry bark which comprisedorganic and inorganic material. The net yield of organic solids derivedfrom the bark was 9.4% of the weight of the oven-dry bark. The inorganicunconsumed S0 was 13.4% of the solids in solution. The dry product had amethoxy content of 1.9%

The net yield of organic solids is a measure of the 6 Example IV Inorder to determine the effectiveness of the subject phosphate-modifiedtannin composition a series of tests were conducted using steel heattransfer tubes and coupons and using various test waters. The flow ratein all of the tests was 2.0 g.p.m. (gallons per minute). The tests wererun at a pH of 6.0 to 6.5 and at a temperature of 125 F. unlessotherwise needed. The tests were run for 14 days-four days at hightreatment dosages and ten days at maintenance dosage. A completedescription of the test procedure is set forth in Materials Protection,vol. 1, pages 23 to 30, October 1962. In the tests the following waterswere used:

No. 1400 p.p.m. hardness CaCO No. 3-138 p.p.m. hardness CaCO -I-Al O SiOand Fe The formulations used in the tests include the followingrFonnula- Component P.p.m.

tion

N o. 1 Calcium lignosull'onate 40. 0 Sodium tripolyphosphate. 25. 82-ruercaptobenzothiazole. 2.0

N o. 2 Rayfio* (a bisulfited tannin produced by the 20.0

method set out in Example I I).

Tetrasodium pyrophosphate 28. 0

% sodium 2-mercaptobenzothiazole. 8. 0

Zinc sulfate monohydrate. 5. 6

No. 3 Sodium lignosulfonate 20.0 Tetrasodium pyrophosphate 28.0

50% sodium Z-mercaptobenzothiazole... 8.0

Zinc sulfate monohydrate 5. 6

No. 4 Rayfio* (a bisulfited tannin produced by the 20. 0

method set out in Example III).

'Ietrasodium pyrophosphate. 28.0 2rnercaptobenzothiazole 2. 0

*This bisulfited tannin was dark reddish brown in color and was in theform of a free flowing powder. The chemical analysis of the material inpercent by weight is as follows: Na, 90; K, 0.1; Ca, 0.3; Fe, 0.03; Cu,0.002; Mn, 0.02; Methoxyl, 1.4; Phenolic hydroxyls, 7.8; Sugar, 0.0;Moisture, 4.0. pH of 1.0% aqueous solution, 8.2.

The results obtained using the subject formulations are 45 set forth inthe following table.

TABLE Dosage, p.p.m. as P0 Deposit, Corrosion, Formulation M Waterrug/cm. MPY

Hi Lo bark material which goes into the product solution and isdetermined by the formula where Y is the percent not yield, S is theweight of the total solid content of the liquor, S is the weight ofinorganic salt employed in the process and W is the weight of oven-drybark treated.

A higher yield of reaction product in a more concentrated solution wasobtained by expressing the reaction product in a press, and separatingthe same from the pulpous bark residue under a pressure of about 200lbs. per sq. in. A portion of the solubilized products of digestion areincluded in the bark residue, but nevertheless being water soluble arereadily removed from the bark on forcing out the occluded solution as inthe expressing operation.

As is apparent from the above table, Formulations 2 and 4 are muchsuperior to Formulations 1 and 3. A com- 60 parison between Formulations1 aand 2, for example, at

a dosage level of 30 ppm. shows that the deposit in mg./cm. is 45.5 forFormulation 1, whereas it is only 2.5 for Formulation 2. Using water No.3, Formulation 1 at 60 ppm. level had a deposit in mg./cm. of 14.1,whereas Formulation 4 at the same level using the same test water had adeposit of only 3.2 mg./cm. during the same time period and under thesame conditions.

The substitution of the products prepared as shown in Examples I and IIfor the modified tannin used in Example III produces comparable results.Where it is desired As was pointed out above, the use of the combinationof phosphates and modified tannins provides highly advantageous resultsin inhibiting corrosion and fouling of metal surfaces coming in contactwith cooling waters. Modifying the tannin reduces itssuceptibility toinactivation by iron. Furthermore, the modified tannin substantiallyprevents the depletion of phosphates which is caused by reaction withiron or aluminum hydroxide.

Obviously many modifications and variationsof "the invention ashereinbefore set forth may be made without departing from the spiritandscope thereof, and therefore only such limitations should be. imposed asare indicated in the appended claims.

I claim:

1. A corrosion inhibiting composition .for use in cooling waters whichcomprises in combinatonz' (1) a bisulfited water dispersible tannin,said tannin having been disulfited by reaction with a material selectedfrom the group consisting of ammonium bisulfite, sodium bisulfite, andpotassium bisulfite at a temperature of from 50 C. to about 200 C. forfrom about 0.5 hour to about/1.0 hours, and

(2) pyrophosphate, the ratio by weight of the materials being from about1:4 to 4:1, said bisulfited water dispersible tannin having beencondensed with formaldehyde.

2. A process for inhibiting the corrosive action of cooling waters whichcomprises: adding to said cooling waters (l) a bisulfited waterdispersible tannin, said tannin having been bisulfite'd by reaction witha material selected W from the group consisting of ammonium bisulfite,sodium bisulfite, and potassium bisulfite at a temperature of from 50 C.to about 200 C. for from about 0.5 hourto about 7 4.0 hours, and (2)pyrophosphate, the ratio by weight of the materials being from about'lz4to 41-1, said pyrophosphate being added in sufiicient quantity toprovide a phosphate concentration of-from 1 to 100 ppm. expressed as P0said bisulfited tannin having been condensed with formaldehyde.

References Cited r' 7 I V o ALEXANDER H. BRODMERKEL, Primary Examiner.

L. B. HAYES, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION atent No.3,375,200 March 26, 1968 Reed 8. Robertson It is certified that errorappears in the above identified patent and that said Letters Patent arehereby corrected as shown below:

Column 2, lines 51 and 52, "silutions" should read solutions Column 4,line 16, "any" should read and Columns 5 and 6, in the last column ofthe second table, insert 15 a heading Days in the same table, sixthcolumn, line 6 thereof, "9.9" should read 9.7

Signed and sealed this 25th day of November 1969.

[SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents

1. A CORROSION INHIBITING COMPOSITION FOR USE IN COOLING WATERS WHICHCOMPRISES IN COMBINATION: (1) A BISULFITED WATER DISPERSIBLE TANNIN,SAID TANNIN HAVING BEEN DISULFITED BY REACTION WITH A MATERIAL SELECTEDFROM THE GROUP CONSISTING OF AMMONIUM BISULFITE, SODIUM BISULFITE, ANDPOTASSIUM BISULFITE AT A TEMPERATURE OF FROM 50*C. TO ABOUT 200*C. FORFROM ABOUT 0.5 HOUR TO ABOUT 4.0 HOURS, AND (2) PYROPHOSPHATE, THE RATIOBY WEIGHT OF THE MATERIALS BEING FROM ABOUT 1:4 TO 4:1, SAID BISULFITEDWATER DISPERSIBLE TANNIN HAVING BEEN CONDENSED WITH FORMALDEHYDE.